Hi All,

I have recently started working with Houdini Flip and while trying to achieve air bubble inside Flip simulation in a pouring liquid, I am failing quite miserably. I have used Air Incompressibility but unable to achieve the air bubbles while pouring the liquid something similar to https://www.facebook.com/particleskull/videos/1987853528104282? [www.facebook.com]

Apart from that, I have a few questions and I am very hopeful that I will receive my answers here.

When I reduce particle separation (high particle count) my collision fails and in order to fix it, I reduce grid size and increase iterations too. So my question is how should I proceed, What should I tweak first grid size or iterations so that I achieve a better collision?

In the attached scene file I intentionally used low particle count in order to view and block out my sim but less particle count often cause my collision to fail, Is there any other way to achieve it so that I can save processing time with high particle count?


My vessel (object) does have some thickness to it but sometimes collision fails, don't understand how can I control it and what if I needed a thin geometry in my shot, How can I make collisions to work with thin geo?

Is there any correlation between the particle count or particle radius? e.g If I increase particle count then should I decrease particle radius considering the water-like liquid.

How can I get rid of a few particles which got stuck with the surface of the vessel though the rest of the simulation works perfectly fine?

I'm still learning FLIP myself but seeing that no one has replied yet I thought I'd share a few thoughts from playing around with your hip file.

I can get your set up to produce air bubbles by doing the following:
- Set the grid scale to 2
- Set the particle separation to 0.007
- Turn off surface tension and stick on collision

In particular, the air incompressibility effect didn't become apparent until the particle separation dropped below a certain size. As for your static object collision geometry, I found that you could increase the division size to 0.01 and get the same result with faster simulation times. The issues you are experiencing with failed collisions isn't because your collision geometry isn't sufficiently high-res. The help card for the FLIP solver (https://www.sidefx.com/docs/houdini/nodes/dop/flipsolver.html) has some suggestions for dealing with collisions with very thin surfaces. Perhaps you could set up your collision geometry to have much thicker walls if you don't need to simulate water overflowing the top of the glass.

The other issue you seem to be struggling with is volume loss caused by high velocity particles slamming against a collision surface. I guess that's why you lowered the grid scale significantly but doing so seems to affect the sim significantly in ways I don't yet understand. Maybe someone else can chime in here.

ziconic
I'm still learning FLIP myself but seeing that no one has replied yet I thought I'd share a few thoughts from playing around with your hip file.

I can get your set up to produce air bubbles by doing the following:
- Set the grid-scale to 2
- Set the particle separation to 0.007
- Turn off surface tension and stick on collision

First of all, thank you for answering my questions where others failed to reply, you at least tried your best to reply. I would like to let you know I tried what you have mentioned but unfortunately, my sim failed miserably, it neither generated bubbles nor respected geometry collision, all it created was a splash ignoring collision.

Thank you once again for your effort and I hope some other artist might also share their views and suggestions which could work.

You didn't see splashing inside the bottle as the water flowed out with the settings I suggested? That's pretty much what air incompressibility gets you out of the box. Anything fancier will probably require a much higher res sim with a lot of tuning and art directing….

I think I should ask about it in some other Forum, I was not expecting the kind of response I had received here. I appreciate ziconic tried his best to help me but unfortunately it didn't work.